1. Field of the Invention
The present invention relates to a system and method for controlling mechanically-driven musical instruments, and in particular to a system and method for controlling the drive of actuators in a mechanically-driven piano or other instrument.
2. Background of the Technology
Beginning with the invention of pneumatically-driven reproducing pianos in the early twentieth century, systems and methods have been developed for recording music played by a human pianist and for reproducing that music on a piano. Many of these systems and methods have attempted to reproduce not only the temporal sequence of notes played by the pianist, but also their dynamics or the sharp contrasts and subtle shadings in loudness that help to make piano performances pleasing. The overall problem of reproducing dynamics can be divided into two distinct parts: recording the dynamics played by a pianist, and recreating these dynamics on a piano.
The problem of recording the dynamics played by a pianist is addressed, for example, in U.S. Pat. No. 4,307,648 to Stahnke issued Dec. 29, 1981, which is hereby incorporated by reference in its entirety. However, there is an unmet need in the art for improved systems and methods for recreating the recorded dynamics.
In an application such as a mechanically-driven piano, recorded music is recreated, for example, using solenoids or other actuators. One actuator is provided for each key of the piano. Each actuator controls the movement of one piano key to recreate recorded music. The actuators may be operated at various speeds to recreate the dynamics of the recorded music.
The actuators may be situated below the back ends of the keys and driven by electrical signals reproduced from a recorded medium, thereby depressing the keys as if they were played by a human pianist. The loudness of each note may be controlled by the drive provided to the actuator for the corresponding key. For example, if a loud note is desired, a larger drive is provided to the actuator, and the actuator is operated at a relatively fast speed. The key is depressed quickly and a relatively loud note is played. In contrast, if a soft note is desired, a smaller drive is provided to the actuator, and the actuator is operated at a relatively slow speed. The key is depressed more slowly and a relatively soft note is played.
In many prior art systems, the actuators are solenoids. A solenoid may consist, for example, of a drive coil, a moveable ferromagnetic plunger movably inserted through a bobbin of the drive coil, and a yoke and polepiece that contain the drive coil and form a magnetic path.
The keyboard of a piano is arranged to accommodate a human hand. If the actuators were configured side by side in a single row underneath the keys, the size of the actuator would be severely limited. Consequently the maximum force that it would be able to produce would also be limited, and loud passages could not be accurately reproduced. Thus, in some systems, the actuators are arranged in a staggered manner so that the size of each solenoid can be increased, as required to play loudly.
The actuators may be staggered vertically (with one row of solenoids above another) or horizontally (in the front-back direction). A vertically-staggered arrangement of solenoids is shown, for example, in U.S. Pat. No. 4,121,491 to Wilkes. A horizontally-staggered arrangement of solenoids is shown, for example, in U.S. Pat. No. 4,741,237 to Murakami and Tajima. Both arrangements are shown in U.S. Pat. No. 3,426,304 to Cannon and Morse.
As shown in FIG. 1 (Prior Art), staggering the solenoids vertically allows the plungers (not shown in FIG. 1) and plunger extensions 106, 118 to be arranged in a single row. This arrangement has the advantage of providing a uniform lever advantage for keys of the same color, but there are two disadvantages: the solenoids 116 protrude beneath the piano in an unsightly way, and the lower row or rows of solenoids 116 suffer from having long plunger extensions 118 that may become cocked, which compromises the ability to play softly.
A horizontal arrangement of the solenoids is shown in FIG. 2 (Prior Art). This arrangement allows an installation that is nearly invisible, because the solenoids 35 can be mounted with most of their height concealed within the keybed. In addition, the plungers 12 are supported within the bobbins 30 very close to the keys, eliminating the long plunger extensions required by a vertical arrangement. However, the fact that the plungers 12 are staggered along the length of the keys causes the lever advantage of the front row to be less than the lever advantage of the back row or rows.
In the vertically-staggered arrangement shown in FIG. 1, there are two different lever advantages. The black keys have their pivotal axes further toward the rear of the keys than the white keys, creating a larger lever advantage. Thus, applying a drive to an actuator beneath a black key results in a dynamic different from the dynamic that results from applying the same drive to a solenoid beneath a white key. This discrepancy results from the physical construction of the piano. If the design of the actuator is such that its velocity is substantially independent of force for a given drive, a black key will play more softly than a white key. On the other hand, if the actuator design is such that its force is substantially independent of velocity for a given drive, a black key will play more loudly. For solenoids of conventional construction, force is largely independent of velocity for a given drive and a black key will play more loudly.
In the horizontally-staggered arrangement, there are four different lever advantages. In addition to the inherent discrepancy between the black and the white keys, there is an additional discrepancy resulting from the horizontally-staggered arrangement itself. Plungers in the front row strike the keys closer to their pivotal axes, so the lever advantage is smaller. Plungers in the back row or rows strike the keys further from their pivotal axes, so the lever advantage is larger. Thus, for a horizontally staggered-construction with two rows, there are four different lever advantages (white keys in the front row, black keys in the front row, white keys in the back row, black keys in the back row). For arrangements with three or more horizontally-staggered rows, the number of lever advantages increases. For solenoids of conventional construction force is largely independent of velocity for a given drive, and keys played by solenoids in the back row will play more loudly than similar keys played by solenoids in the front row.
There is an unmet need in the art for an improved method for driving actuators that overcomes the inaccurate dynamics that result from multiple lever advantages.